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New Member

Broadcast over VLANs

We are using layer 3 switch 3750(standard image) to connect all VLANs. We need to enable one PC to receive broadcast from server that is on different VLAN. How can we do that? Multicast? but it sounds like 3750(standard image) not support multicast. Is any way to allow controlled broadcast traffic cross VLAN?

Thanks,

S.Cole

7 REPLIES
Cisco Employee

Re: Broadcast over VLANs

You could use a "ip helper-address" to forward broadcast traffic from one subnet to another.

The UDP destination port must be for TFTP, Domain Name System (DNS), Time, NetBIOS, ND, BOOTP or DHCP packet, or a UDP port specified by the ip forward-protocol udp global configuration

For more information about the "ip helper-address" command, refer to the following URL:

http://www.cisco.com/en/US/products/sw/iosswrel/ps5207/products_command_reference_chapter09186a00801a7ea5.html#wp1091304

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: Broadcast over VLANs

The command "ip helper-address" is probably what we need to do, but I can not find this command under interface configure mode. Its IOS version is 12.1(14)EA1a-SMI. Based on document, it should have.

Thanks for your help.

S.Cole

Cisco Employee

Re: Broadcast over VLANs

The SMI image is L2 only. You need a EMI (L2/L3) image if you want to be able to forward packets between different VLANs.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: Broadcast over VLANs

3750smi is L3 switch and it has rip protocol. The routing function is working okay. Probably I need to ask Cisco which version of IOS supports "ip helper-address".

S.Cole

Cisco Employee

Re: Broadcast over VLANs

My bad, the smi does support L3. I got confused with some other image I guess. The image you heve does support the "ip helper-address" command.Have you done a "no switch port" on the interface before you tried to apply this command.

Thanks,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Cisco Employee

Re: Broadcast over VLANs

BTW: the command is "no switchport" not "no switch port".

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: Broadcast over VLANs

Thank you very much. It solved the problem.

I get time today to try it and it works!

S.Cole

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